In this study, Linear Elastic Fracture Mechanics (LEFM) approach is used to evaluate the fatigue strength of a box-shaped welded structure. A parametric study is also undertaken to study the effect of various weld parameters on the fatigue strength, such as lack of weld metal penetration, load position, and plate thicknesses. FRANC3D software was adopted to obtain the stress intensity factor values for two types of full-length and intermediate crack sizes, located at the critical region of the weld of the box-shaped structure. It was concluded that the LEFM approach could capture the crack propagation from the weld root reasonably well under the given conditions and estimate residual fatigue life of the welded structures conservatively. Compared to fatigue life estimations by nominal stress method (1,714,564 cycles) or effective notch stress method (63,385 cycles), the LEFM approach can estimate the residual life more accurately. Especially for intermediate (4 mm) lack of penetration (LOP) of weld metal case (589,198 cycles) in comparison to the experiments (1,216,595 cycles). The parametric study showed that the fatigue life increases with increase in the thickness of flanges, lesser LOP in the weld root, and when load is applied more toward the center of the plate.

中文翻译：

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箱形焊接结构的断裂力学和疲劳寿命评估：有限元分析和参数设计

在这项研究中，线性弹性断裂力学（LEFM）方法用于评估盒形焊接结构的疲劳强度。还进行了参数研究，以研究各种焊接参数对疲劳强度的影响，例如缺乏焊接金属熔深，载荷位置和板厚。采用FRANC3D软件获得位于箱形结构焊缝临界区域的两种全长和中等裂纹尺寸的应力强度因子值。结论是，在给定条件下，LEFM方法可以较好地捕获焊缝根部的裂纹扩展，并保守地估计焊接结构的残余疲劳寿命。与通过标称应力法估算的疲劳寿命（1,714，564个周期）或有效的缺口应力法（63,385个周期），LEFM方法可以更准确地估计剩余寿命。与实验（1,216,595次循环）相比，尤其是对于中间（4毫米）焊缝金属外壳（589,198次循环）缺乏熔深（LOP）的情况。参数研究表明，疲劳寿命会随着法兰厚度的增加，焊缝根部的LOP减小以及向板中心施加更多载荷而增加。